It's not a terrible expansion, just to pick up on the points from the post above.
New way to play - it is a new way to play, sort of, whilst exploring and rescuing civilians/other soldiers still features you also have to defend your base from a two-wave zombie onslaught periodically. So not only do you have to go and forage for supplies, but you need to keep one eye on the threat meter and make sure you can get back to defend your base in time!
Hardware - You do start out with assault rifles and handguns, as well as a random melee weapon. As each base attack is survived, the military will drop you in another care package which sometimes contains better weaponry. You can also request a weapons drop etc. with enough respect.
Don't expect something radically different to Breakout, the new map is fun but it's no bigger than the old one and no more functional. There isn't really anything amazingly new to see or do, and on this map you DO NOT move base - you get the one, with upgrade slots, which does kill the thrill of exploring and finding somewhere new to call home.
At the end of the day, it's cheap. You'll get your money's worth out of it whilst you wait for the developers to do something a little more fun.